[API] Fix -Werror=alloc-size-larger-than= warning in runtime_context.h (open-telemetry#3709)

Author: marcalff

api/include/opentelemetry/context/runtime_context.h

@@ -241,6 +241,26 @@ class ThreadLocalContextStorage : public RuntimeContextStorage
   {
     friend class ThreadLocalContextStorage;
 
+    /**
+     * Limit the max stack depth.
+     * The stack will still work beyond this limit,
+     * counting push() and pop() properly,
+     * but will not record contexts.
+     *
+     * In practice, this should not affect instrumented applications,
+     * the limit is set to 1 million nested scopes.
+     *
+     * The whole reason for this limit to exist is to prevent
+     * compiler warnings like:
+     *   error: argument 1 value ‘18446744073709551615’
+     *   exceeds maximum object size 9223372036854775807
+     *   [-Werror=alloc-size-larger-than=]
+     * on this line of code:
+     *   Context *temp = new Context[new_capacity];
+     * when compiling with gcc and optimizations (-flto).
+     */
+    static constexpr size_t max_capacity_ = 1000000;
+
     Stack() noexcept : size_(0), capacity_(0), base_(nullptr) {}
 
     // Pops the top Context off the stack.
@@ -250,6 +270,11 @@ class ThreadLocalContextStorage : public RuntimeContextStorage
       {
         return;
       }
+      if (size_ > max_capacity_)
+      {
+        size_ -= 1;
+        return;
+      }
       // Store empty Context before decrementing `size`, to ensure
       // the shared_ptr object (if stored in prev context object ) are released.
       // The stack is not resized, and the unused memory would be reutilised
@@ -278,6 +303,10 @@ class ThreadLocalContextStorage : public RuntimeContextStorage
       {
         return Context();
       }
+      if (size_ > max_capacity_)
+      {
+        return Context();
+      }
       return base_[size_ - 1];
     }
 
@@ -286,6 +315,10 @@ class ThreadLocalContextStorage : public RuntimeContextStorage
     void Push(const Context &context) noexcept
     {
       size_++;
+      if (size_ > max_capacity_)
+      {
+        return;
+      }
       if (size_ > capacity_)
       {
         Resize(size_ * 2);
@@ -299,8 +332,14 @@ class ThreadLocalContextStorage : public RuntimeContextStorage
       size_t old_size = size_ - 1;
       if (new_capacity == 0)
       {
+        // First increase
         new_capacity = 2;
       }
+      if (new_capacity > max_capacity_)
+      {
+        // Last increase
+        new_capacity = max_capacity_;
+      }
       Context *temp = new Context[new_capacity];
       if (base_ != nullptr)
       {